1) Field of the Invention
The present invention relates to a process and an apparatus for continuously producing polyester type polymers such as polybutylene terephthalate and polyethylene terephthalate.
2) Related Art
Since polyethylene terephthalate (hereinafter referred to as PBT) resins are excellent in the crystallizing characteristic and also excellent in mechanical properties, electric characteristics and heat resistance, they have been used for applications such as electric machines, electronic parts, mechanical parts and automobiles and their demand has been increased steadily.
Heretofore, for the general PBT production process, a terephthalic acid alkyl ester comprising dimethyl terephthalate as a main ingredient and a glycol comprising 1,4-butanediol (hereinafter referred to as BD) as a main ingredient are placed at an appropriate ratio in a mixing vessel, a transesterification catalyst is added and conditioned and then they are sent to a transesterfication reaction vessel set to a predetermined reaction temperature by a pump. In the transesterification reaction, two or three stirring vessels with stirring blades are disposed in series and methanol formed as reaction by-products, and tetrahydrofuran (hereinafter referred to as THF) formed by decomposition of the methanol formed as reaction by-products and BD and water are separated in a distillation tower. Then, a polymerization catalyst is added and the process proceeds to the polymerizing reaction step. At first, vertical stirring vessels or horizontal stirring vessels are disposed in plurality for the prepolymerization step and, further, a horizontal stirring vessel is disposed as a final polymerization step. In the vessels for the polymerization step, a condenser is disposed for removing BD, THF and water formed as reaction by-products and the step is operated in a reduced pressure atmosphere at high temperature. In the existent continuous PBT reaction step, the number of the reaction vessels is 4 to 6, a stirring blade and a power source therefor are installed in each of the reaction vessels, and a distillation column or a condenser for separating and removing the reaction by-products are disposed.
In these production steps described above, since the products are exposed in a reaction state at high temperature for a long time, a portion of the resin formed by polymerizing reaction is broken at the bond sites by thermal decomposing reaction to lower the degree of polymerization and increase the acid value of the resin (carboxyl group concentration at the terminal end of the polymer), to worsen the quality. Further, since the polymerization step is operated in an reduced pressure atmosphere, it is necessary that the evacuation unit has to be operated by an additional device, and high maintenance cost and high installation cost are required for the operation of the apparatus.
An object of the present invention is to improve the well known processes for producing a high molecular weight polybutylene terephthalate with improved efficiently for the entire apparatus and economical operation upon energy saving throughout the plant facility.
An object of the present invention is to improve the prior art described above and provide a continuous polycondensation apparatus and a continuous polycondensation process for efficiently producing polymers of favorable moldability excellent in heat stability and resins of excellent hydrolysis resistance with minimum energy while suppressing thermal decomposition during production of the resin with necessary minimum reactors constitution.
The foregoing objects can be attained by using terephthalic acid (hereinafter referred to as TPA) and BD as the starting material for the production of PBT, conducting the direct esterifying reaction step and the polymerizing reaction step in three or four reaction vessels, thereby minimizing the number of vessels requiring stirring power and shortening the residence time to minimize the heat hysteresis at high temperatures during production of the resin and decreasing the number of unreacted terminal carboxyl groups in the resin.
Typical embodiments of the present invention are summarize below.
(1) An apparatus for continuously producing polybutylene terephthalate, which comprises a first reactor for reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient, thereby producing an oligomer with an average degree of polymerization of 2.2 to 5, a second reactor for polycondensating the oligomer from the first reactor, thereby preparing a low polymerization product with an average degree of polymerization of 25 to 40, and a third reactor for further polycondensating the low polymerization product from the second reactor, thereby producing a high molecular weight polyester with an average degree polymerization of 70 to 130 with good heat stability and excellent hydrolysis resistance, or an apparatus for continuously producing polybutylene terephthalate, which comprises a first reactor for reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient, thereby producing an oligomer with an average degree of polymerization of 2.2 to 5, a second reactor for polycondensating the oligomer from the first reactor, thereby preparing a low polymerization product with an average degree of polymerization of 25 to 40, a third reactor for further polycondensating the low polymerization product from the second reactor, thereby producing a high molecular weight polyester with an average degree polymerization of 70 to 130, and a fourth reactor for further polycondensing the polyester from the third reactor to an average degree of polymerization of 150 to 200, thereby producing a high molecular weight polyester with good heat stability and excellent hydrolysis resistance, characterized in that (i) reactors without any stirrers by an external power source is used for the first and second reactors, (ii) the first reactor is an approximately cylindrical vessel type reactor having an inlet and an outlet for a process solution at lower parts, respectively, of the vessel proper and an outlet for volatile matters and reaction by-products at the upper part of the vessel proper, and having a calandria type heat exchanger formed in the longitudinal direction of the vessel proper and near the inside wall of the vessel proper and being immersed in the process solution, the process solution supplied into the vessel proper at the inlet at the lower part thereof is heated to a predetermined reaction temperature by the heat exchanger and is stirred and mixed by spontaneous connection due to a density difference caused by a temperature difference between the formed volatile by-product gas and the process solution, (iii) the second reactor is an approximately cylindrical vessel type flow reactor in a double cylinder structure having an inner cylinder opening in the vessel and an inlet for the process solution at the lower part of the double cylinder structure, the process solution passing through tubes of a shell and tube type provided on the outside of the inner cylinder of the double cylinder structure and thereby heated to a predetermined temperature and passed upwardly to the level of the inner cylinder opening and then flowing down through the inner cylinder and the vessel proper being provided with an outlet for volatile matters and reaction by-products at the upper part thereof, (iv) the third reactor is a horizontal cylindrical vessel type reactor having an inlet and an outlet for a process solution at lower parts on one end and an another end in the longitudinal direction of the vessel proper, respectively, and an outlet for volatile matters at the upper part of the vessel proper, and a stirring rotor rotating in the proximity of the inside wall of the vessel proper is provided in the longitudinal direction of the vessel proper, the stirring rotor in the vessel proper is provided with a plurality of stirring blade blocks in accordance with the viscosity of the process solution and the stirring blades are without any rotating shaft along the center of the stirring rotor, and (v) the fourth reactor is a horizontal, approximately cylindrical vessel type reactor having an inlet and an outlet for a process solution at lower parts an one end and an another end in the longitudinal direction of the vessel proper, respectively, and an outlet for volatile matters at the upper part of the vessel proper, the reactor has two stirring rotors rotating in the proximity of the inside wall of the vessel proper in the longitudinal direction of the vessel proper, and the rotors each have stirring blades.
(2) A process for continuously producing polybutylene terephthalate, which comprises a first step of reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient in a first reactor, thereby producing an oligomer with an average degree of polymerization of 2.2 to 5, a second step of polycondensing the oligomer from the first step in a second reactor, thereby preparing a low polymerization product with an average degree of polymerization of 25 to 40, and a third step of further polycondensing the low polymerization product from the second step in a third reactor to an average degree of polymerization of 70 to 130, thereby producing a high molecular weight polyester with good heat stability and excellent hydrolysis resistance, or a process for continuously producing polybutylene terephthalate, which comprises a first step of reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient in a first reactor, thereby producing an oligomer with an average degree of polymerization of 2.2 to 5, a second step of polycondensing the oligomer from the first step in a second reactor, thereby preparing a low polymerization product with an average degree of polymerization of 25 to 40, a third step of further polycondensing the low polymerization product from the second step in a third reactor to an average degree of polymerization of 70 to 130, thereby producing a high molecular weight polyester, and a fourth step of further polycondensing the polyester from the third step in a fourth reactor to an average degree of polymerization of 150 to 200, thereby producing a high molecular weight polyester with good heat stability and excellent hydrolysis resistance, characterized in that reactors characterized by (i), (ii), (iii), (iv) and (v) described in the foregoing (1) are use; the aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof and the glycol comprising 1,4-butanediol as a main ingredient are supplied to the first step in a molar ratio of the former to the latter of 1:1.7 to 1:30, and the first step is carried out at 220xc2x0-250xc2x0 C. and 33 kPa-150 kPa, the second step at 230xc2x0-255xc2x0 C. and 100 kPa-0.133 kPa and the third and fourth step each at 230xc2x0-255xc2x0 C. and 0.665 kPa-0.067 kPa; the stirring blades of the third and fourth reactors are rotated in a range of 0.5 rpm-10 rpm; total reaction time for the first to the third steps is in a range of 4-7.5 hours, or total reaction time for the first to the fourth step is in a range of 6 to 8.5 hours; a slurry of the aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof and the glycol comprising 1,4-butanediol as a main ingredient prepared in a ratio of the former to the latter of 1:1.7 to 1:3.0 is supplied to the first step upon admixture of an esterifying catalyst or a polymerization reaction catalyst; and another third reactor or a plurality of third reactors is provided in parallel to the third reactor in the third step, thereby producing different kinds of polybutylene phthalate with different degrees of polymerization from that produced in the main line of the third and fourth reactors or adjusting operating conditions of each of a plurality of the third reactors to increase kinds, precise quality control and production rate of polybutylene terephthalate.